Recently, InGaN-based, blue light-emitting diode chips have been developed, and it is well known that such blue light-emitting diode chips exhibit high light emission brightness.
Such a blue light-emitting diode chip can be utilized for producing white light by coating the surface of the chip with a light-pervious synthetic resin containing a fluorescent material. In this manner, part of the blue light emission is converted into yellow light by the fluorescent material in the coating, and their mixture results in the white light.
In the case where the blue light emitted from a blue light-emitting diode chip is subjected to wavelength conversion for white light emission by coating the chip with a coating of a light-pervious synthetic resin containing a fluorescent material, the degree of the wavelength conversion largely depends on the thickness of the coating. For instance, when the thickness of the coating is relatively large, the ratio of wavelength conversion into yellow green becomes high so that a yellow green tone becomes strong. When the thickness of the coating is relatively small, the ratio of wavelength conversion of blue light becomes low, so that a blue tone becomes strong. Therefore, it is necessary to make the thickness of the coating generally uniform with respect to a plurality of LED chips and to make the surface of the coating smooth and flat.
In the above-described structure, the tone of the white light can be changed by changing the thickness of the coating.
JP-A-2000-208822 as a prior art discloses some methods for coating a blue light-emitting diode chip with a light-pervious synthetic resin containing a fluorescent material. According to the methods:
(1) A plurality of LED chips are mounted on the upper surface of a substrate at a pitch which allows the formation of a predetermined coating on side surfaces of the LED chips, and then a light-pervious synthetic resin layer containing a fluorescent material is formed on the upper surface of the substrate to embed the LED chips in the synthetic resin layer, and then portions of the synthetic resin layer between the LED chips are removed by photolithography (a technique which performs printing by light exposure using a pattern mask and developing);
(2) A plurality of LED chips are mounted on the upper surface of a substrate at a pitch which allows the formation of a predetermined coating on side surfaces of the LED chips, and then a light-pervious synthetic resin containing a fluorescent material is applied to each of the LED chips by screen printing using a mask to coat the LED chip with the synthetic resin;
(3) A plurality of LED chips are mounted on the upper surface of a substrate at a pitch which allows the formation of a predetermined coating on side surfaces of the LED chips, and then a light-pervious synthetic resin layer containing a fluorescent material is formed on the upper surface of the substrate to embed the LED chips in the synthetic resin layer, and then the substrate and the synthetic resin layer are diced into individual LED chips.
In the above-described prior art methods (1) and (2), to change the thickness of the coating to achieve an intended white tone in the light emission, the pattern mask for photolithography or the mask for screen printing need be replaced with one having a pattern pitch capable of achieving an intended thickness.
Therefore, as the pattern mask for photolithography or the mask for screen printing, different kinds of masks need be prepared depending on the number of intended tones, which costs much and results in considerable increase in the manufacturing cost.
Further, by the photolithography of the method (1) and the screen printing of the method (2), irregularities are inevitably formed at the surface of the coating covering the LED chip, and the surface cannot be made a smooth flat surface. Therefore, the tone of the light becomes non-uniform.
In the method (3) of the prior art, the surface of the coating is provided by dicing, so that a smooth flat surface can be provided. In this method, however, to change the thickness to change the tone, the spacing distance between the LED chips need be changed in mounting the LED chips on the substrate. Therefore, changing of the tone is extremely troublesome and requires much cost.
Patent Document 1: JP-A-2000-208822.